In today's multi-function world, ever smaller integrated circuit packages are packed with feature delivering semiconductor devices. For instance a processor chip for a cell phone will include the processor, ROM, RAM and peripheral devices for power management and I/O. Each of these functions has its own state of the art technology or manufacturing “sweet spot”. The result is several different technology nodes might be assembled in a single package.
The initial driver of such a packaging technology was computer memory. As the state of the art improved and reliability of multi-die packages improved, other functions started to be drawn into the packaging revolution. All manner of functions were joined in a single package. At first manufacturers tried to maintain the same technology types in a single package. As these packages were successful and the demand for additional functions reached a crescendo, companies started mixing different technology nodes in the same package. An analog bipolar die could be packaged with a CMOS microprocessor, or a 0.13 μm communication switch could be packaged with a 0.25 μm oscillator circuit.
The success of the mixed technology packages opened the industry to innovative packaging schemes that stack or parallel multiple chips and sometime include embedding other packaged devices in the larger package. In these approaches, the interconnect can be through flip chip attach, wire bond or other internal substrates. Many of these devices are very complex. They deliver a complete function in a single integrated circuit footprint, significantly simplifying the printed circuit board design. As the bounds of innovation were pushed and more elaborate package stacks were attempted, manufacturing and reliability issues came to the fore. In some cases the yield issues made the packages too difficult to bring to full production.
Many of the reliability issues are a result of component movement during the many thermal transitions of the assembly process. As substrates and integrated circuit die are heated for attach processes and wire bonding, they have a tendency to warp and flex from their resting position. Bond wires can interfere with the solder mask on the edge of a buried substrate in the module. The result can be broken connections or reduced pull strength on the bond wires. Both of these effects result in an inoperative device or one with reliability problems.
Thus, a need still remains for an assembly process and apparatus that will allow reliable interconnects to the buried stacking module. In view of the increasing demand for multiple integrated circuit packages, it is increasingly critical that answers be found to these problems. In view of the ever-increasing need to save costs and improve efficiencies, it is more and more critical that answers be found to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.